Heretofore, means for feeding data to a system by using means responsive to touch connected to a data input of a data processing system in such a manner that the data displayed may be altered under the control of the data processing system is known. For example, in U.S. Pat. No. 3,482,241 to E. A. Johnson there is disclosed a plurality of touch-sensitive contacts including a transparent screen placed adjacent the screen of a cathode-ray tube, which may be selectively actuated for indicating which portion of the image on the cathode-ray screen is to be examined in further detail. When activated, data indicating which sensitive contact is touched is applied to a computer or the like where it is used typically, to control the display device.
This type of prior art touch display generally includes an aggregation of elements necessary to create it, thereby making them quite complex and detailed, hence making the system quite expensive. In addition, noise characteristics may be such that it is impossible to distinguish the actual signals from background noise. Also, the aggregation of elements may introduce reliability problems.
Another type of known prior art which relates specifically to touch sensitive cathode-ray tube switches is the switch described in U.S. Pat. No. 3,958,239 to R. E. Green. This patent teaches that touch sensitive contact pads comprise a series of areas in a matrix across the screen of a cathode-ray tube. The matrix, in turn, is coupled to a diode matrix for decoding purposes. Following decoding, which decodes the coordinates of the matrix area touched, the system incorporates a computer or the like responsive to the decoded output which is unique to the display device or cathode-ray tube for controlling this system. Here again, a disadvantage is that an aggregation of elements necessary to create the system makes the system expensive. Additionally, this system, as well as the previously mentioned system, suffers from the fact that voltage offset errors are present. This is an extremely important parameter when it is desired to operate on an analog signal under direction of a logic signal. Also, the latter system is not noise immune.